I think you are correct on your assumptions. Fiber is a good thing ,but we over do it. I'm still not sure why someone would take fiber for leaky gut.
I think adding EFA's will assure good bowel movement. Cod liver oil,Fish oil caps and small amounts of flax seed oil.
I once knew a person who we called the "fiber King" he wa scared to death about colon cancer. His diet was bascially all fiber. He would even eat the stalks of brocolli.. raw.
He ended up having surgery to remove a blockage he had acquired through his non-stop fiber ingestion.
Now that is an extreme example,but I think as you state,that supplemental fiber will cause alot of gas,bloating and constipation in alot of people.